Would like to resurrect this thread, as it is might be the solution I have been looking for.

I need to provide 120V, very low distortion sine wave at 100W. The load is mostly pure resistance, with a smaller load of rectifier-capacitor at around 0.15A AC.

Have tried the ferroresonant route, hoping the mostly resistive load would help the PS produce a cleaner sine wave, but this wasn't the case. Odd harmonics still there, and at much too high of levels.

Had success with an oscillator feeding a class AB amplifier, which actually worked quite well, but the heat dissipation in the amplifier was just too high. The amp was rated at 850W bridged, and I couldn't drive a 60W load through a 24-120V transformer for more than a few minutes before the heat sink temperature really started to rise. If I can't find another solution, I may just have to buy a cheap 2000W amp and let the fan run.

This perfect sine product has some real potential, but it looks like it's still in prototype stages. Is this a product that is available for purchase, and if so, how much and how to buy?

If the frequency of the 100W sine wave is below about 1KHz. Then a class D amplifier is your solution. Yes switching amplifiers have their share of problems, but they are well understood and traditional solutions now exist for almost all of them

Please define:
Frequency of output.
Definition of "low" distortion.

(Before all you class D advocates circle in for a kill, I know that it's possible to achieve higher output frequencies, but distortion products do rise and efficiencies do drop, making it a far more difficult solution for the moderately skilled.)

Thanks for the reply. The frequency will be 60Hz. I am needing to run the filaments of DHT's with a very low distortion sine wave, eliminating as much as possible IMD and other nasties. Please, no recommendations to use DC; at this point, I know what I want. (DC maybe someday, but only if I fail at using AC- I learn by failure)

As far as "low distortion", I would expect better than 0.25%, which is the specification for an Elgar type source. With the Wein bridge and audio amp, I am expecting better than 0.1%, though I haven't measured it directly. Looks extremely clean to the naked eye.

Harmonic spectrum would be worthy of note, too. The low order harmonics tend to be more problematic for me, since it is easier to filter out the kHz and above spectra. Just the use of the audio amp feeding into the transformer eliminates the high frequency garbage.

That amp from PE has merit, and any suggestions for Class D or G amps are welcome. What I don't know, however, is what kind of dissipation / cooling they will need.

Power is 273 watts out. E^2/R = 273 so E = 48 Volts RMS, you would need a step up transformer if you want 120V or maybe a step down to the actual filament Voltage. Your preference for AC filaments is a good one, except for possible issues with hum. Usually filaments run on DC have a shorter life.

Since the unit is rated at 273 watts out at an efficiency of around 75% it would appear it can dissipate about 200 watts. Other than the output voltage this unit would probably do your task.

Like I said others also make these things in many sizes and if you have the time and skills you can make your own.